System and method for controlling refrigeration loop expansion valve flow and compressor speed under conditions of rapid heat load changes

Abstract

A hybrid controller for a thermal control unit for controlling the temperature of a device under test (DUT) is described that uses information from an in independent heat-injecting control loop as a fast-responding proxy for relative changes in DUT test head load. This information provides additional feedback to the refrigeration sub-system's controller(s), resulting in achieving the overall system goal of temperature control of the DUT over a wide range of set point temperatures and the rapidly changing DUT head load.

What is claimed is: 
     
         1 . An apparatus for controlling a temperature of a device under test, the apparatus comprising:
 a heater sub-system that includes a heater controller, the heater controller configured for providing a heater injection signal for controlling a heater;   a refrigeration sub-system that includes an expansion valve flow controller, the expansion valve flow controller configured for controlling, based on an error of the heater injection signal compared to a nominal heater injection signal, a flow of liquid refrigerant to a variable flow expansion valve.   
     
     
         2 . The apparatus of  claim 1  wherein the refrigeration sub-system includes a compressor speed controller configured for controlling, based on the error of the heater injection signal compared to a nominal heater injection signal, a speed of a compressor. 
     
     
         3 . The apparatus of  claim 1 , wherein the expansion valve flow controller includes a feedback controller configured to receive an additional input from an evaporator superheat temperature sensor. 
     
     
         4 . The apparatus of  claim 1 , wherein the expansion valve flow controller includes a tuned feedback controller configured to regulate refrigerant flow based on the heater injection signal error and a secondary evaporator superheat error signal. 
     
     
         5 . The apparatus of  claim 4 , wherein the tuned feedback controller is a proportional-integral-derivative (PID) controller. 
     
     
         6 . The apparatus of  claim 1 , wherein the compressor speed controller includes an adaptive filter configured to smooth transient fluctuations in compressor speed adjustments based on the heater injection signal error. 
     
     
         7 . The apparatus of  claim 1 , further comprising a compressor suction inlet; wherein the expansion valve flow controller is further configured to prevent liquid refrigerant from reaching the compressor suction inlet by adjusting flow based on a detected superheat threshold. 
     
     
         8 . The apparatus of  claim 1 , wherein the refrigeration expansion valve controller utilizes the heater injection signal to modulate the expansion valve flow such that the heater remains within a controllable operating range. 
     
     
         9 . The apparatus of  claim 1 , wherein the refrigeration sub-system further includes a secondary cooling loop that is activated by the heater injection signal error, providing additional cooling capacity. 
     
     
         10 . An apparatus for controlling a temperature of a device under test (DUT), the apparatus comprising:
 a heater sub-system including a heater controller, the heater controller configured to generate a heater injection signal to control a heater based on a temperature difference between the DUT and a setpoint temperature;   a refrigeration sub-system including an expansion valve flow controller and a compressor speed controller, the expansion valve flow controller configured to adjust a flow of liquid refrigerant through a variable flow expansion valve based on an error of the heater injection signal relative to a nominal heater injection signal, and the compressor speed controller configured to adjust a speed of a compressor based on the heater injection signal error, wherein the heater injection signal serves as a proxy for DUT heat load changes, allowing the refrigeration sub-system to rapidly respond to variations in the DUT heat dissipation.   
     
     
         11 . The apparatus of  claim 10 , wherein the compressor speed controller is further configured to dynamically adjust compressor speed based on variations in the heater injection signal error, wherein the adjustment reduces thermal oscillations and prevents compressor overloading. 
     
     
         12 . The apparatus of  claim 10 , further comprising an evaporator superheat temperature sensor;
 wherein the expansion valve flow controller includes a tuned feedback controller configured to receive an additional input from the evaporator superheat temperature sensor.   
     
     
         13 . The apparatus of  claim 10 , further comprising a secondary evaporator superheat error signal;
 wherein the expansion valve flow controller includes a tuned feedback controller configured to regulate refrigerant flow based on the heater injection signal error and the secondary evaporator superheat error signal.   
     
     
         14 . The apparatus of  claim 13 , wherein the tuned feedback controller is a proportional-integral-derivative (PID) controller. 
     
     
         15 . The apparatus of  claim 10 , wherein the compressor speed controller includes an adaptive filter configured to smooth transient fluctuations in compressor speed adjustments based on the heater injection signal error. 
     
     
         16 . The apparatus of  claim 10 , further comprising a compressor suction inlet;
 wherein the expansion valve flow controller is further configured to prevent liquid refrigerant from reaching the compressor suction inlet by adjusting flow based on a detected superheat threshold.   
     
     
         17 . A method for regulating the temperature of a device under test (DUT), the method comprising:
 receiving a measured temperature of the DUT and determining an error relative to a setpoint temperature;   generating, by a heater controller, a heater injection signal based on the determined temperature error;   adjusting, by an expansion valve flow controller, the flow of liquid refrigerant to a variable expansion valve based on an error of the heater injection signal relative to a nominal heater injection signal;   adjusting, by a compressor speed controller, a speed of a compressor based on the heater injection signal error; and   controlling the refrigeration sub-system to dynamically balance cooling and heating operations such that the heater remains within a nominal operating range, preventing temperature oscillations, evaporator flooding, and compressor overheating.   
     
     
         18 . The method of  claim 17 , further comprising dynamically tuning the expansion valve flow controller to prioritize rapid response to DUT heat load changes while preventing excessive refrigerant flow. 
     
     
         19 . The method of  claim 17 , wherein adjusting the speed of the compressor comprises applying an exponential smoothing function to filter noise from transient heater injection signal fluctuations. 
     
     
         20 . The method of  claim 17 , further comprising regulating refrigerant flow by a tuned feedback controller based on the heater injection signal error and a secondary evaporator superheat error signal.